In answer to the actual OP heading ~ "... which be the most important one FFS procedure" I NOW feel, - after chin reduction and facelift – and not having had done anything about the forehead, brow-bossing... et al, - the forehead seems VERY important. VERY!
Is this because I got the bottom part of my face done? It's not easy to say, as I clearly did not like how my chin changed, had become more and more prominent during the later years of my life. It actually had bugged me, long before Transition was on my mind. In profile I thought I looked a bit like a 'Nutcracker' and I found this to be a simply too strong a feature – though not immediately noticeable from the front view. Take a second look at my avatar you might just get what I'm trying to say.
Now, there are females, always older ones, that have prominent chins.
Yet, I still have to see one, older or younger, that has the more typical kind of male brow-bossing/brow-ridge. And believe you me, I look, and look, and then some. Brow-bossing must count as one of THE most unusual facial features with the vast majority of females. Caucasian and Asian.
It is just so different to note, once one has become aware of this male feature, and much more so, with Caucasian male features - I NEVER consciously took note of it before.
I now think that forehead contouring is actually THE most important of FFS. But it is ALSO the most invasive, no doubt about that - for me.
It will be interesting for me to hear if anyone has a different experience. It be really interesting.
Axélle